The present application relates to oil from water separators and, more particularly, such separators suitable for use in inground or aboveground installations where it is desired to prevent oil in water concentrations above a predetermined limit from being distributed to the environment in an uncontrolled fashion.
Mechanical oil from water separator systems are known. Devices/systems are also known that provide settling in chambers separated by bafflesxe2x80x94refer the arrangement of FIG. 1 which shows a Prior Art American Petroleum Institute (API) oil from water separator design. It consists of a rectangular tank with two or more vertical partitions or baffles to separate entry chamber, oil disengagement chamber and effluent water chamber, and which is designed to run full of water.
The API oil from water separator is sized to provide low turbulence conditions and sufficient residence time for oil globules with a minimum diameter of 0.015 cm (150 microns) to separate from the oil/water mixture flowing though the separator.
This prior art system can be characterised as a decant-type system where for every input of liquid there is an output of a similar amount at the same time, thereby affecting separation efficiency.
Attempts have been made in the prior art to control the level of the oil/water interface, for example see U.S. Pat. No. 5,147,534 (Rymal) and U.S. Pat. No. 4,031,007 (Sierra) and, more generally, see U.S. Pat. No. 4,960,513 (Young), U.S. Pat. No. 4,436,630 (Anderson) and U.S. Pat. No. 5,378,353 (Koch).
In all of these systems, whilst there has been a move away from a simple decant-type approach, there is usually added a specific oil from water separation process beyond mere gravitational separation. Koch requires a specific separate coalescer unit whilst U.S. Pat. No. 4,554,074 (Broughton) utilises separation plates.
In many applications it would be desirable to employ a separator system having the intrinsic simplicity of the API-type systems whilst achieving consistent predetermined levels of separation of oil from water.
It is an object of the present invention to provide an inherently simple oil from water separator system which provides consistent levels of separation of oil from water over a predetermined range of inflow conditions.
Accordingly, in one broad form of the invention there is provided an oil from water separator including an oil disengagement chamber adapted to receive an oil and water mixture and retain it for a sufficient time in a relatively undisturbed state whereby oil in the mixture floats to the top of the mixture resulting in a substantially oil free volume of water having a layer of oil derived from said oil and water mixture floating on the surface thereof; said oil disengagement chamber partially separated from an effluent water chamber by an under flow baffle which ducts said substantially oil free volume of water to said effluent water chamber; said oil from water separator characterised in that outflow of said substantially oil free volume of water from said effluent water chamber is limited by flow retarding means to a rate of outflow which is a function of the head of the liquid in said effluent water chamber.
In a further broad form of the invention there is provided an oil from water separator including an oil disengagement chamber adapted to receive an oil and water mixture and retain it for an extended time in a relatively undisturbed state whereby oil in the mixture floats to the top of the mixture resulting in a substantially oil free volume of water having a layer of oil derived from said oil and water mixture floating on the surface thereof; characterised in that outflow from said chamber is controlled in a predetermined way by flow retarding means.
In a further broad form of the invention there is provided an oil from water separation system including an oil disengagement chamber having a flush storage volume defined between a chamber high liquid level and a chamber low liquid level; a liquid volume equivalent to said flush storage volume caused to exit from said chamber on attainment of said chamber high liquid level.
Preferably said flush storage volume is caused to exit by means of a siphon mechanism.
In a further broad form of the invention there is provided an oil from water separator including an oil disengagement chamber adapted to receive an oil/water mixture and retain it for a sufficient time in a relatively undisturbed state whereby oil in the mixture floats to the top of the mixture resulting in a substantially oil free volume of water having a layer of oil derived from said oil and water mixture floating on the surface thereof; characterised in that outflow from said chamber is prevented until said mixture reaches a predetermined chamber high liquid level whereupon said volume of water is caused to exit said chamber.
In a further broad form of the invention there is provided an oil from water separator including an oil disengagement chamber adapted to receive an oil/water mixture and retain it for a sufficient time in a relatively undisturbed state whereby oil in the mixture floats to the top of the mixture resulting in a substantially oil free volume of water having a layer of oil derived from said oil and water mixture floating on the surface thereof; characterised in that outflow from said chamber is limited by flow retarding means to a predetermined function of the level of said oil and water mixture in said chamber.
Preferably said flow retarding means is operable only between a chamber low liquid level and a chamber high liquid level.
In one particular preferred form said flow retarding means comprises at least one siphon which primes at said chamber high liquid level and loses prime at said chamber low liquid level.
In an alternative preferred form said flow retarding means comprises at least one bleed aperture or weep hole.
Preferably said at least one bleed aperture or weep hole is located at the level of said chamber low liquid level.
More preferably said at least one bleed aperture or weep hole is sized with reference to expected inflow of said oil and water mixture into said oil disengagement chamber such that, during operation, the level of said oil and water mixture will rise from said chamber low liquid level up to a higher liquid level and then return to said chamber low liquid level, thereby defining for each situation an oil and water mixture active lag capacity or accumulation capacity between said chamber low liquid level and said higher liquid level.
More preferably said active lag capacity or accumulation capacity has a characteristic which is a function of
(a) inflow rate
(b) desired residence time of said oil and water mixture in said oil disengagement chamber.